texts: Why the forbidden lines of [OIII],[NII] and [SII],[OII] are sensitive to electron temperature and electron density, respectively?

texts:
I am trying to understand the topic of "Metallicity estimates", either HII regions or planetary nebula. For this latter, the electron temperature (and density) must be known. I am studying the formalism of Osterbrock.

I know, for instance, that if you use the lines [OIII]4363 and [OIII]5007 the electron temperature can be computed. In the same way, the ratio between [OII]3729 and [OII]3726 provides an estimation of electronic density.

Actually, I also know that, for the case of [OIII], its metastable excited states are relatively separated. For the case of [OII], such metastable excited states are very close. Such separation, in the metastable excited states, is crucial to compute the temperature and density.

My point is that I do not understand why this separation is important, from a physical point of view. Why the ratio between these lines can estimate such properties?

You can check examples of what I am talking about in "Electronic Density" and "Electronic Temperature" sections of this link: http://www.astronomie-amateur.fr/feuilles/Spectroscopie/NGC2392.html

I hope to make me understood.

Thank you very much for your help.


texts: Have we actually seen a black hole out there? By "seen" I mean "recorded a em-spectrum image of gravitational lensing caused by object believed to be black hole".


texts: what is the acceleration parameter in a universe?

texts:
Obtain the value of the acceleration parameter in a universe, including cosmological radiation and constant.
what is the exactly acceleration parameter in a universe means ?


texts: Are there any bodies in the solar system whose rotation is almost tidally locked or barely tidally locked?

texts:
The Moon's rotation is firmly tidally locked to the Earth and the Earth's rotation is firmly tidally unlocked with respect to the Moon. I gather that Mercury's rotation is tidally locked in a 3:2 resonance - which sounds a little precarious. Are there any bodies which are on the verge of being tidally locked (very nonuniform rotation) or are barely tidally locked (very large libration)?  Are there any bodies whose rotation is actually chaotic for such reasons?
[Edit] Note, this question is about the physical libration rather than the apparent or optical libration caused by the body being observing from different perspectives.


texts: I can see several stars in the sky they can make a line come from the West south and going to East north direction at the time between 6.50 to 7.00 pm Indian time on date 13.1.20. What might these three stars be?


texts: What do "star noise" and "sky noise" refer to for TESS (Transiting Exoplanet Survey Satellite)?

texts:
The eoPortal article for TESS (Transiting Exoplanet Survey Satellite) gives a fairly in-depth summary of the space telescope design and planned operation. Some further background information on its observation mode and orbit can be found in the video linked below.

Based on the caption (also shown below), I'm guessing that "star noise" is possibly related to shot noise; the counting statistics of the incoming photons or perhaps the photoelectrons thereby produced, and "sky noise" is the cumulative effect of all the other actual light present in the spatially binned area of a given star, including Zodiacal light within the solar system as well as all other sources.

If so, and even if not, I don't really understand the units of $\sigma$ as parts per million per square-root hours, and why sky noise would vary as $I^{-1}$ while star noise expressed in these units varies as $I^{-1/2}$, where $I$ is the intensity of the light from a given star.

below: Figure 12: Top: Expected 1σ photometric precision as a function of stellar apparent magnitude in the IC band. Contributions are from photon-counting noise from the target star and background (zodiacal light and unresolved stars), detector read noise (10 e-), and an assumed 60 ppm of incorrigible noise on hourly timescales. Bottom: The number of pixels in the photometric aperture that optimizes the signal-to-noise ratio (image credit: TESS Team)

Excellent background on TESS: https://youtu.be/mpViVEO-ymc


texts: Why don't we feel the speed of earth moving

texts:
When we move our vehicle, we "feel" the speed of it. However, when stationary, we still are moving,but moving by quiet a speed. We know that earth moves with X speed, our own solar system moves at Y speed. etc.
Why do we not feel this speed? Even sitting at my home, my mind must be gyrating at an incredible speed.


texts: How to measure distances to stars by means of spectroscopic parallaxes?

texts:
How to measure distances to stars by means of spectroscopic parallaxes on practice?
What is the accuracy of measuring distances using this method compared with distances based on HIPPARCOS trigonometric parallaxes? My sample of objects consists of A-B type stars.


texts: What is the maximum distance measurable with parallax?

texts: What is the furthest star or celestial object whose distance has been calculated with parallax and how does it compare to the theoretical limit using today's telescopes? And how exactly does telescope aperture relate to the maximum distance measurable (other than the bigger the aperture the bigger the distance)?


texts: Term for the moment when hydrogen fusion begins in a star

texts: I have read of this process many times, but I don't think I know the term specifically for the moment when hydrogen fusion begins. What is this moment called?


texts: Visibility of human activity on the moon

texts:
In this video the host of Test Tube Plus states that

you can go out a buy a laser, point it at the moon, and see the retroreflector left by the astronauts.  When you point at the right spot you'll see a reflection, elsewhere not.  He reiterates that this is not just a hypothetical use of 2nd person for effect, but that you the viewer can go out and try this yourself, and anyone paying any attention to moonlanding conspiracy theories ought to try it
tracks and artefacts at the landing site can be seen with amateur telescopes, and again this is approachable to anyone who cares to look

Neither of these seem correct to me.  Could someone with real numbers weigh in on this?

I seem to recall that seeing artefacts is only possible in the latest high-res images taken from lunar orbit, and the telescope that uses the reflector gets back single photons on some trials and is a much more powerful laser than you could buy!  But, a continuous beam may be different? How big of a laser would you need to see a reflection with a viewing instrument that doesn't cost more than the laser?


texts: Are binary stars with only one visible sibling common enough to contribute noticeable to dark matter?

texts:
Single-lined spectroscopic binaries is a binary system where only one star can be detected.
Are they common enough to contribute noticeable to dark matter?


texts: Which star with a Bayer designation is the farthest from the Sun?

texts: The key to finding the answer seems to involve processing data from astronomical databases, which I'm not sure how to do in this case. I'd prefer to limit the answer to the original list of approximately 1500 stars, but answers that rely on a list that contains stars with more recently acquired designations could be interesting to consider as well.


texts: Is radar interferometry used, or feasible, for ground based astronomy?

texts:
I've heard of "interferometric synthetic aperture radar" being used for Earth observation from satellites and airplanes. Is active radar used interferometrically for astronomical purposes too? Such as characterizing asteroids or space debris, or identifying volatiles in the polar craters of Mercury.

Unfortunately for this idea, Arecibo and FASTare located 173 longitudinal degrees apart and have limited fields of view, so they can't observe the same object simultaneously.


texts: Clearing the Neighbourhood: Definition of 'Orbital Region'?

texts:
I am trying to determine how wide a 'neighbourhood' a planet is expected to clear.

However, the Wikipedia article on the matter provides no clarity, simply stating that a planet is expected to clear it's 'orbital region' with no definition provided.

I suspect that the correct answer is that a planet is expected to clear a region around it's orbit equal to the radius of its Hill Sphere, but I am not certain of it.

Furthermore, for a planet of Earth mass, the Hill Sphere radius is a measly 0.01AU, which doesn't seem like much of a neighbourhood!

Is there a formal way to define the 'neighbourhood'?


texts: There are Asteroids "trapped" in Jupiters Langrange points 4 and 5 called trojans and greeks. Are there any asteroids in the earths L4 and L5? Have we seen asteroids in Lagrange points of the earth and moon system? Why are only L4 and L5 stable and L1, L2 and L3 require corrections to remain at those positions?


texts: Can we see the stars at the edge of the Milkyway?

texts:
This question proved much more difficult to formulate than I initially imagined. It concerns how far out in the Milky Way that we actually see with different telescopes. I know the Milky Way disk is about 100k light years wide, its halo a couple of times that wide, and most of the naked eye stars are within 1000 light years. I also know that when many stars are close together they are more visible, which means we can easily see for example the double cluster in Perseus at about 7000 light years with our naked eyes. But if you take a large telescope and peer into the distance, how easily do you see through the star fields until the point where you have no more foreground stars in the field of view, and all that is there are the numerous faint galaxies lurking in the back. For example, in the Hubble Deep field you see a few stars. Are we looking at the last few stars at the edge of the Milky Way, or are there more hidden in the field that we can't see because they are too far away/too faint?

I realize that there are dust clouds in the Milky Way obscuring the view, so if you look towards the galactic center you would definitely not see all the way to the other side. But lets assume we're looking perpendicular to the galactic plane. Lets also say that you're using a 16" telescope, allowing you to see maybe down to the 15th magnitude. Do you see the stars at the edge of the galaxy?

Another way of approaching the question... From what I've read it seems we estimate the Milky Way to contain about 250 billion stars. I also read that the Gaia satellite will map about 1 billion stars. Does that mean our best telescopes are only able to discern 1/250 of the stars in the Milky Way? Of course all stars on the other side the galaxy disk are hidden from us, so they surely account for a large portion of the invisible stars. But looking straight up from the galactic plane, can we see the last galactic stars before the empty intergalactic "void"?


texts: Why is it said that the far side of the moon's crust is thicker?

texts:
This video states that NASA has determined that the far side of the moon's crust is thicker than the near side's crust. How did they determine this?

Please note I'm not asking for theories or hypotheses on how this came to be, but rather if the difference in thickness indeed is measurable scientifically today.

[So off-topic: If it is in fact true, I favour the theory that the centrifugal force of the earth's gravity along with the fact that the far side is always pointing outwards, is responsible for this and not some other moon smashing into our moon etc. as is shown in that video.]


texts:
I'm trying to realistically approximate the value of meteor sightings during a meteor shower because I don't want to have high expectations going in. I have a couple questions about this formula I found from this site

Number of meteors=ZHR×sin(θ)/(F×r^6.5−m)

Question 1
I would like to know for the calculation of F, where

F=1/(1−k)
where k is the fraction of the sky which is which you cannot see, because it is obscured by cloud or other obstructions such as trees.

Assuming I am on a flat plain with no trees/building whatsoever and I have a clear view from 0-180 degrees (cross section view of the earths crust). Will k be 0.5 based on the fact that I cannot see whats below ground (180-360 degrees).
Also will the limitation of the human eye affect this value? I.e If I am facing north my peripheral vision can only reach maybe north east to north west hence further increasing k value above?
Question 2
What value should I have for m in the above formula if I am at this location? I currently assume a value of 6 according to this wiki. Is this right?


texts: Looking for a Solar System Simulator including the smaller celestial body, for macOS

texts:
I am researching for a sci-fi novel that will happen in 2136. For this I would like to know specific positions of "smaller" celestial bodies in our Solar System.
An example can be the dwarf planet Ceres and other big rocks in the Main Asteroid Belt.

There will be a lot of traveling in the Inner Solar System and I need to know the relative distances between two objects.

If possible, I would like the tool to be open-source.

Edit: I am looking for a tool like NASA's Eyes. That tool can give a detailed and global view on the Solar System. It has the orbits of different bodies. It also lets me play with time and distance. And most importantly, it can give me the distance between two bodies (https://eyes.nasa.gov/).

The main problem with NASA's app is that it only let me travel to until 2050 :/


texts: What would be the best inertial reference frame to describe objects in the solar system (other than the solar system's barycenter)?

texts:
For the purpose of a project, I require the components that describe the inertial frame to be as independent as possible from solar system bodies itself. Since the solar system barycenter is itself determined by the positions and masses of the solar system bodies, it will not be a good choice.

I was thinking that the frame that I want could be described by some nearby star that does not have planets of its own or else the galactic centre itself.

If such an inertial frame exists, I would like the same to be expressed in heliocentric cartesian coordinates.

Any relevant thoughts would be much appreciated!


texts: Night-Day Cycles in S-Type Planetary Systems

texts: I am a writer and space enthusiast. For a story I am currently writing I would like to have a planet which orbits a star which resembles the sun, which in turn orbits another star. In this situation there would be multiple types of "days" including "bright day," when both suns are visible, "dim day," when only the further sun is visible, and "day," where only the nearer sun is visible. Is there any way to determine how this cycle would work? Any formulas or papers done? If so, what information would I need to have to figure it out? Thank you.


texts: In rocky planets,does fast rotation cause flatting or low flatting imply slow rotation?

texts:
As far as I know, Venus and Mercury have 0 flatting, but Mars and Earth have detectable flatting, and Venus and Mercury are both rotating slowly. I'm confused as to the relation between rotational speed and flatting.

Does rotation cause a rocky planet to be flat? Or zero flatting implies Venus and Mercury rotate slowly? Which is correct?


texts: I also see the line of 30 stars @today(11/jan/2020)on5:35am

texts: I can't take any pic because I don't know how many light are coming.


texts: Is there any data source for the rotational axes of bodies in the solar system?

texts:
I have found several right ascension and declination coordinates for the poles of bodies in the solar system, but there seems to be no comprehensive source that is easily uncovered with Google etc. containing any other than those of the planets and a handful of other bodies.

Most importantly i am missing them for the Moon, but i'd like them for all regular satellites and any other bodies if possible.


texts:
I'm just getting started with very primitive analysis of FITS data, and I have a 'raw' FITS file which I don't know how to get different wavebands of data from (if this is even possible).

Filename: casa_raw.fits
No.    Name         Type      Cards   Dimensions   Format
0    PRIMARY     PrimaryHDU      33   ()
1    EVENTS      BinTableHDU    793   14621280R x 19C   [1D, 1I, 1I, 1J, 1I, 1I, 1I, 1I, 1E, 1E, 1E, 1E, 1J, 1J, 1E, 1J, 1I, 1I, 32X]
2    GTI         BinTableHDU     28   2R x 2C      [1D, 1D]

Could anyone explain what exactly this information conveys?


texts: What kind of star would allow for life like our Sun/Earth and then go nova?

texts:
In the Star Trek Prime Universe, Star Trek:  The Original Series, the home stars of the Fabrini, Platoans and Sarpeidons went nova, while in Star Trek:  The Next Generation one of the stars in the Bynar system (which might have been a multiple system) went supernova.

What type of star would allow sentient life to evolve to an advanced level, roughly to the same as twenty-first century Earth, and then go nova.


texts: Can we detect exoplanets with perpendicular plane of ecliptic?

texts:
If I understand correctly, all the current exoplanet search is based on planets transitioning the distant star.

If the plane of ecliptic of that star happens to be perpendicular to line of sight from Earth to that star - or sufficiently inclined, so that orbits of all its planets as seen from Earth "circle" the star without ever transitioning it - does that mean we're completely unable to detect them?


texts:
The Phys.org news item Hubble is the ultimate multitasker: Discovering asteroids while it's doing other observations mentions the Hubble Space Telescope's use of parallel fields:

A couple years ago, the NASA/ESA Hubble Space Telescope was observing very distant galaxies, some of them billions of light years away. It was part of the Frontier Fields Project (FFP,) an ambitious observing program which aimed to observe six massive galaxy clusters. The FFP pushed Hubble to its limits.
[...]
This image is a couple years old now, and it shows what's called the parallel field for the Abell 370 galaxy cluster, about 4 billion light years away. It's called a parallel field because of the technique used to capture it.
A press release explains parallel fields this way:
"While observing each cluster with one of the cameras on Hubble, the team also used a different camera, pointing in a slightly different direction, to photograph six so-called 'parallel fields." This maximised Hubble's observational efficiency in doing deep space exposures, imaging a myriad of far away galaxies."

Question: How are "parallel fields" implemented on the Hubble Space Telescope? How are two cameras able to take different exposures in different directions at the same time? What optical components points them in different directions?


texts:
I am reading about the interior temperature structure of Jupiter. It says in various texts that there are regions in Jupiter's atmosphere which are well-approximated by a dry adiabatic lapse rate.

Does this mean that in these regions there is convection happening? Is adiabatic just a general synonym for convection?


texts:
This post answers what is Mars' gravity at its highest point (Olympus Mons) compared to the Earth's and Mars' standard, it's 0.3736 g (Mars standard is 0.3794 g). This also seems to be the lowest gravity anywhere on Mars. Mercury has a similar surface gravity to that of Mars, and I'm trying to figure out the gravity at Mercury's highest point (which also may be the lowest gravity anywhere on the planet).
Mercury's mass are 3.3011e+23 kg and Mercury's mean radius are 2439.7 km. This results in a surface gravity of 3.7014 m/s² or 0.3774 g. Mercury's highest elevation is 2.78 mi (4.48 km) above what is considered the sea level. So I add these 4.48 km to the mean radius which results in 2444.18 km, thus the gravity would be 3.688 m/s² or 0.3761 g. Since Mercury rotates extremely slowly, I guess any difference in latitudinal gravity is tiny enough so we can neglect it here as well as any equatorial bulge (the highest point is close to the equator). However, there may still be differences in mascons.
Did I make any mistake? Do we know whether any mascons are to be considered? If I'm right, Mars' lowest gravity is lower than Mercury's lowest one, despite Mars' average gravity being higher than that of Mercury.


texts:
In Space.com's Dr. Pulsar and Mr. Magnetar? 2 Star Types May Turn into Each Other (and in the linked video) "Tom Prince, a physics professor at the California Institute of Technology and a senior research scientist at NASA's Jet Propulsion Laboratory" is quoted as saying:

  First, magnetars don't last long — just a year to a few years, before colossal waves of X-rays dissipate the magnetic energy...

and Wikipedia's Magnetar says:

  A magnetar is a type of neutron star believed to have an extremely powerful magnetic field (∼1013 to 1015 G, ∼109 to 1011 T)1. The magnetic field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays2.

  1https://arxiv.org/abs/1703.00068

  2Rare Earth: Why Complex Life Is Uncommon in the Universe. Springer. ISBN 0-387-98701-0.

Question: How does the field decay of a magnetar power the emission of high-energy electromagnetic radiation?

More specifically:

Is it as simple as $\partial \mathbf{B} / \partial t$ produces an electric field which accelerates charged particles that happen to be there, and then those accelerating particles radiate photons?
Does the energy radiated by these photons cary any significant fraction of the total energy in the field?
Is the word done producing these photons the reason that the magnetic field decays?


texts: As we know, some stars can fuse heavy elements to produce carbon and oxygen after using up hydrogen if they are massive, and the remnant of stars are usually hot, my question is, if a star fuse to produce carbon and oxygen, does it also burn to produce carbon dioxide?


texts: What was the size of the universe around 400 million years after the Big Bang?

texts:
I was trying to find out how large the universe was around 400 million years after the Big Bang as this is when some of the first galaxies were formed but I am having trouble finding out the answer or working it out.
I found some information on the size of the universe after 380,000 years when the CMB was created and by calculating the red shift from the time of creation a size of roughly 80 million light years is given by reducing the observable universes size by a factor of 1100 but I am not sure how to use this to calculate the universes size after 400 million years and I am not sure if as the above calculation is for the observable universe how that related to the actual size.
Is the size of the universe in terms of its length or diameter known or can be calculated after 400 million years from the Big Bang event?


texts: Is there a more permanent way to set up an Artificial Horizon?

texts:
For the last few months we have been constantly setting up an Artificial Horizon (Davis Instruments) using motor oil as the liquid.   We discovered that it is very hard to take a reading off of it unless we wait at least 15 minutes for the oil to become perfectly still.
We tried leaving it in place and covering it with a 5-gallon bucket.  This doesn't work very well as the glass covering it fogs up.   When we try to dry the glass, the oil begins moving and we are back to waiting 15 minutes.  We tried using it without the glass covers, but discovered that this only works when there isn't any wind.   We live on top of a mountain, there is always wind.
Googling "Permanent Artificial Horizon" and other various wordings has not helped.
We intend to use this spot at least twice daily.  We hope to learn to use the sextant as a navigational tool.  However, we are mainly combining the sextant, compass & watch to mark the position of objects we see through the telescope so that we can record them in our Astronomy Diaries.  Our telescope doesn't do this for us.
Waiting 15 minutes or more for the oil to stop moving is proving to be a pain in the rear because it has to be done so often.   Has anyone figured out a way to permanently set up an artificial horizon that can be left in place?


texts: How to calculate a planet's apparent size when the planet is viewed from a moon in orbit around it?

texts:
Specifically in this case, how large would Jupiter be seen in the Io's sky in comparison to the moon in the Earth's sky? How to calculate this?

Also, if somebody knows any online software which lets you input moons and planets to see how their sky looks like to also fill in the answer, it's appreciated.


texts: As a black hole passes through spacetime, does it affect it?

texts:
Nothing in the universe stands still. It's always on its way from somewhere to somewhere. A black hole follows a trajectory through the universe, moving from one locus in spacetime to another locus.
Deep inside each black hole is a point that we've never been able to characterize.My question is, does the singularity, and possibly the powerful gravitational fields around the singularity have any measurable effect on the area of spacetime it passed through? One imagines an undeformed area of spacetime. After some time, a black hole passes through this spacetime, then moves on. Does the spacetime it passed through simply go back to being everyday, garden variety undeformed spacetime?


texts: The matter anti matter asymmetry is still a mystery that still can't be explained. But what if there wasn't an asymmetry? Isn't it possible that there was exactly equal amounts of matter and anti matter which did in fact annihilate each other, and the energy released from it was converted into mass? I know this arises a lot of paradoxes like if so what kind of matter is everything then . I guess what I really want to know more about is, after a Matter and Anti Matter collision, what kind of matter can be created (or rather converted) from the resulting energy outburst?


texts: How would humans with appropriate equipment navigate the surface of Saturn's moon Titan on foot?

texts:
Taking into account the physical characteristics of Titan (e.g. surface gravity, atmospheric pressure), what would be the most efficient method of motion for an astronaut to navigate the surface of Titan on foot?

Would it be a leaping or hopping motion? Or would it make more sense to walk somehow? I'm unsure how the friction of the ground would accommodate for that.

For the purpose of this thought experiment, lets assume that humanity has the necessary equipment to put an astronaut on Titan and to have protective clothing to enable reasonable safety from environmental hazards on the surface.

Thanks in advance!


texts: How large will our Sun get during the red giant phase (ie which planets will it engulf) before the helium flash?

texts: I have read that our Sun will increase in size to a red giant.  But after it goes through the helium flash it will contract somewhat.  Then after that grow again to be even larger before finally losing its outer layer as a planetary nebula and becoming a white dwarf.  I've seen estimates that the red giant phase will consume Mercury, Venus, and probably Earth.  (Even with Earth's expanded orbit due to the Sun losing mass to the solar wind.)  My question is how large will that first stage be prior to the helium flash?  Which planets, if any, will it engulf?


texts: Relation between mass of gas, mass of stars and dark matter halo mass

texts:
As we all know that Mass of the galaxy can be written as the sum of the mass of gas(Mg), the mass of stars (Ms), and mass of dark matter halo(Mh), as
M(galaxy)=Mg+Mh+Ms,
But is there any formula which relates Mg and Mh and, Mh and Ms??
Does anybody know?


texts: What is the current accepted hypothesis of what caused Triton's retrograde orbit around Neptune?

texts:
According to the NASA overview about Triton, this, the largest satellite of Neptune is unique in that it has a retrograde orbit around Neptune.  The page also suggests that Triton is a captured Kuiper Belt object.

What is the current accepted hypothesis as to what caused Triton's retrograde orbit?  Also, is this orbit sustainable - meaning, is it degrading?


texts: Why do degenerate objects get hotter as more mass is added?

texts: After reading this question, I decided to post a question about degeneracy. I've seen simulations on large, $15\text{+ }M_J$ objects that are accreting mass. They do not grow in radius, instead they shrink (that is something I know about degenerate objects). But why do they get hotter? I'm assuming it comes from the internal pressure, and at what mass does some sort of fusion occurs?


texts: Is there any thing special with an axial tilt of roughly 25°?

texts: Half of the planets in the solar system have an axial tilt of $25.5\pm 3^\circ$: earth (23.5°), mars (25.3°), saturn (26.7°) and neptune (28.3°). If random collisions in the early solar system caused the axial tilt of the planets, it seems like there should be a lot more variation in the planetary tilts. Is there some mechanism that favors tilts around 25°, or is this just a statistical fluke?


texts: Setting specific CENTER coordinates coordinate in SWARP

texts:
The SWARP Documentation specifies that we first set the CENTER_TYPE to MANUAL and then in the CENTER parameter we specify either one of the equatorial coordinates (RA, Dec). This is specified in the image below:

In doing so, I do not understand how by giving just one of these coordinates, the SWARP tool will interpret which specific coordinate is given.
I am currently viewing the output image in matplotlib, setting its projection with the wcs header info that we get in the output fits file. It seems as though SWARP takes every coordinate specified in the CENTER parameter as its right ascension. There is also no way to specify if we want to set the declination value. How can we set a center for the output image if

We can only give one coordinate (RA or Dec), and
Whatever coordinate we provide is interpreted by SWARP as the right ascension?


texts: I have a question about the wording in a paper about a planetary system and comets

texts:
I was reading a paper. This is the paper:
https://arxiv.org/abs/2006.01711 (https://ui.adsabs.harvard.edu/abs/2020MNRAS.496.4979D/abstract
In the method section in the second paragraph there is a bit of wording that is confusing to me.

We will examine the dynamics of some Solar System comet analogs3, namely, 2P / Encke, 9P / Tempel 1, and 31P / Schwassmann-Wachmann 2; they are later referred to as comet A, B, and C, respectively, for convenience.

The paper is essentially about a system called 55 cancri. They do simulations about it to look at comet interaction since there is an empty space without planets where there might be comets. They say they examine 3 solar system comets.
Does that mean they just use the regular 3 planets and star in the 55 cancri system and then add 3 comets as an assumption? Or do they do 2 different simulations one for the solar system to test the numerical simulation and then the cancri system?
The confusion also arises since they mention comet analogs. I do not understand what analog means here. They also link to a table with the planets in the 55 cancri system which I do not understand how it relates to this sentence.
Can somebody explain what they mean here?


texts:
I noticed that East and West appear swapped on maps of the Sun, even though the Sun rotates around its polar axis in the same sense as Earth.

See for example below Sun disk with a Venus transit diagram or also here.

So, at least for the Sun, East and West are defined from an Earth observer viewpoint. This makes me wonder: How are East and West defined on other bodies of our solar system?


texts:
High mass x-ray binaries necessarily accrete via wind, no disc accretion?

What makes the difference between a hmxb and a lmxb?

In what kind of circumstances does an accretion disc form?

How does it form?

When do we think there is a disc?

There is a clear cut between disc and wind accretion?


texts: Problems with computing X,Y,Z positions of planets at a certain time in Unity3D (C#)

texts:
I'm trying to create a little program in Unity3D that positions the planets in 3D space at a given time. I've followed this document: http://stjarnhimlen.se/comp/ppcomp.html.

Using the data from section 4 and the code from section 6 and 7 I should have the correct algorithm right? I did skip on the changes in the orbital attributes (eg + 4.70935E-5 * d) because I just need to have them move in a set orbit. I don;t really need them to change over time. For now I'm just increasing the mean anomaly over time without taking the period in account.

The problem is that the planets do not seem to get the correct offset to the ecliptic, and their movement is really weird: they speed up, then slow down and reverse in their paths. Here is a video of their movement: https://www.youtube.com/watch?v=zHOBChFpan0

It looks like the eccentricity is correct on their ellipses and the distances to the sun are also correct, but the rest is just wrong. I'm not that great at math or astronomy to fully understand what's going on in this algorithm, but I'm hoping someone here might spot the error.

using UnityEngine;
using System;

public class Orbit : MonoBehaviour
{
public float longitudeOfTheAscendingNode;
public float inclination;
public float argumentOfPerihelion;
public float semimajorAxis;
public float eccentricity;

public float meanAnomalySpeed = 0.1f;

float M = 0; //mean anomaly

void Update()
{
    SetPosition();
}

void SetPosition()
{
    float N = longitudeOfTheAscendingNode;
    float i = inclination;
    float w = argumentOfPerihelion;
    float a = semimajorAxis;
    float e = eccentricity;

    float E = M + e * (180 / Mathf.PI) * Mathf.Sin(M) * (1 + e * Mathf.Cos(M));

    float xv = a * (Mathf.Cos(E) - e);
    float yv = a * (Mathf.Sqrt(1 - e * e) * Mathf.Sin(E));

    float v = Mathf.Atan2(yv, xv);
    float r = Mathf.Sqrt(xv * xv + yv * yv);

    float xx = r * (Mathf.Cos(N) * Mathf.Cos(v + w) - Mathf.Sin(N) * Mathf.Sin(v + w) * Mathf.Cos(i));
    float yy = r * (Mathf.Sin(N) * Mathf.Cos(v + w) + Mathf.Cos(N) * Mathf.Sin(v + w) * Mathf.Cos(i));
    float zz = r * (Mathf.Sin(v + w) * Mathf.Sin(i));

    transform.position = new Vector3(xx, yy, zz);

    M += meanAnomalySpeed * Time.deltaTime;
    if (M > 360)
        M -= 360;
}

}


texts:
It always was interesting for me to understand the answer for the question:

  What's the reason that we have a different number of days each month?

If the month is fixed on the time that the moon circles the earth, then the time of the circling isn't equal each month? And if the month fixed by the time that the earth circles the sun and then divided by 12 (365:12=30.4), why one month has more days and the other month has less days?

Before desktop computers, how did astronomers handle calculations of dates and times accurately, for example two plates taken decades apart, how would an astronomer calculate the time difference precisely?


texts: Details on the telescope(s) on the Chinese Space Station 天和

texts:
The ISS has a telescope on board. Does the Chinese Space Station have one on board as well?
I heard about Xuntian aka Chinese Space Station Telescope (CSST), but not too many details. Would that be the only telescope? What would be the primary scientific goals?


texts: Why did the big bang not just produce a big black hole?

texts:
Questions I've often wondered about:

If all the matter and energy were concentrated at a single point at the big bang, why wasn't that a black hole, or why didn't it form one?

If the reason #1 above didn't form a black hole is one of several explanations such as inflation or whatever else, then why didn't all the mass and energy form a big black hole at some finite time after this big bang happened?  For instance, I've (possibly incorrectly) heard that inflation made the universe the size of an orange.  Well why didn't it form a black hole then?  Or once the universe expanded to, say, the size of the moon. Why not then? Just insert whatever reasonable size you want in place of "orange" or "moon."  The question is why didn't a black hole form out of all the matter and energy after the Big Bang?


texts: How can I find out the maximum magnification of my telescope?

texts:
I have a Meade DS-2080AT-LNT. It's an inexpensive scope that I've had for several years. It has a couple of eyepieces with it, but nothing that will let you get a really good look at planets. I doubt I can see any Messier objects as more than a blip.

But it's more than good enough to take up and leave at my family's cabin in the far North and I think all of the kids that visit will enjoy it. But to get more out of the scope I was thinking about getting a Barlow lens. I see lenses of 2x and even 5x for sale. I don't know enough about telescopes to know what "x" of Barlow I should get for this scope.

The specs are as follows:

80mm (3.1") Aperture: Plenty of brightness to reveal planets, clusters,
nebulas and more.
Sturdy Fork Mount: Lightweight and solid aluminum mount and
tripod for stable views.
494 AutoStar® Controller: Automatically locates more than 1400 objects
and points the telescope toward them for you at the push of a button.
Series 4000 Super Plössl 1.25" Eyepieces: (26mm and 9.7mm) Enjoy low
and high power viewing with crisp, wide fields of view.
Altazimuth Set-up: Easy-to-use mount moves up/down, left/right.
SmartFinder™/Red Dot Viewfinder™: Makes stars and other objects
easy to find. Electronic level sensor, north sensor, and precision
internal clock help get your scope aligned with the heavens quickly.
AutoStar Suite™ DVD: Amazing planetarium software and instructional
video will help you learn about the night sky and how to use your
telescope. Print out star charts. Plan observing sessions. Displays over
10,000 night sky objects. Operates on any Windows®-based PC

I appreciate any help!


texts: If the Earth is rotating counter clockwise, how does the sun rise from east?

texts:
I was very confused when I watched this video from 2:18 till 2:45. And it seems very clear that if the Earth is really rotating from west to east, shouldn't be the Sun rising from west and setting in east? We all know certainly that the sun rises from east, but how come Earth is rotating in the way as shown in the linked video?

PS: I somehow feel very stupid for asking this question...


texts: Are we really star-stuff from the interior of collapsing stars?

texts:
Carl Sagan has said several times that we are "star-stuff".

One instance can be found in Good Reads' Carl Sagan > Quotes > Quotable Quote:

  The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

Question: Was most of my nitrogen really made in the interior of a star during its collapse? Was my calcium and iron made there as well, and not (for example) in an expanding shell after a supernova?


texts:
complete beginner here, only got into star gazing a few days ago using my friend's telescope and I don't really understand at all what any of the measurements mean.

Anyway, talk about jumping in the deep end, but I'm poking around Nasa's Intergalactic Database, but sadly it's all greek to me: http://ned.ipac.caltech.edu/

Here's a galaxy: NGC 7590

Here's its basic data:

EquJ2000.0 RA

EquJ2000.0 DEC

Velocity km/s

Redshift / z

Magnitude / Qual Filter

Separ arc min

Now I'm afraid I don't really understand what any of these measurements and their values actually mean.

I remember from school what Red Shift is, its the wavelength increasing becoming
'stretched' making the light seem to appear more reddish the faster an object is accelerating away from us. But what is that z unit?

I'm afraid I really don't have a clue regarding anything else... spear arc min, magnitude / qual filter?

Is there a book for a brief understanding of these units? Not out to solve problems regarding celestial mechanics, I just want the NED to make a bit more sense to me so I can visualize these objects.


texts:
this one bothering me,to buy a telescope.
I live in a city,unfortunately with dust and polluted air, is there any affect in viewing a nice capture of our galaxy? Or i need to buy a special telescope?


texts: Can eternal inflation and gravity explain dark energy?

texts:
First of all, I have absolutely no background in astronomy and physics. I just watch a lot of "i-hope-scientific" youtube channels talking about physics and astrophysics and I can kind of follow the maths and concepts.

So, I was thinking, with absolutely no physics to support this:

REAL QUESTION STARTS HERE:

Say, the big bang happened everywhere, followed by inflation that never stopped. This is wat eternal inflation described (if i am correct)

Then, as eternal inflation goes on and more and more universe outside of the observable universe is created. Then there would be an unlimited amount of mass outside our observable universe.

Can this mass create an gravitational effect on the galaxies in our universe?

We are at the center of our observable universe, so the gravitational effect of all the mass outside our observable universe would never affects us. But from the perspective of another galaxy, it would be affected by a bit of universe that is outside our observable universe.

Then you might explain the effect that galaxies that are farther away from us move faster away from us. And that galaxies closer to use move slower away. Then you can explain this by saying that the galaxies farther away are closer to the "unlimited" mass outside our observable universe. And thus are more affected by this. And that galaxies close by are less affected.

The theory with dark energy claims that dark energy causes an outward push from the inside of our universe. Wouldn't this be indistinguishable from a gravitational pull from the outside?

Also, could this explain the red-shift we see in light from the far end of the observable universe? If I remember correct, gravity can red-shift light if the light moves away from the source of the gravitational pull (as seen near black holes). Light form the far end of the universe has moved trough the gravitational pull away from the "infinite mass" of the outside universe.

This was my idea, and I would like to see where I am thinking wrong.

One thing where I obviously might be thinking wrong is that this effect would be homogeneous throughout the universe and it should cancel out. But is this also true when you throw some relativity into the mix?


texts: Would it be possible for life found on moon of rogue planet

texts:
I have heard that there are at least three Basic requirement for life exist in the universe, they are:

Source of Energy
Complex chemistry (including solvent/medium for chemical reaction)
Protection for external threat (e.g. high energy electromagnetic wave, asteroid etc.)

In earth, our major source of energy come from our sun, which provide enough heat to initial chemical reaction in our ocean.

One day, when I was searching the internet, I came upon the ideas of rogue planet, brown dwarf, tidal heating. Which keep me thinking of the possibility of life on the moon of a rogue planet (probability a large gas giant/ brown dwarf).

I have a naive thought on the situation , where the rogue planet radiation and its mass (effect of tidal heating), provide sufficient energy of the moon (hot enough to maintain solvent say water/methane) . And somehow the moon like Titan, which have a dense atmosphere, to protect the surface of the moon.

As I digging deeper, I find some other sources saying that, these kind of situation is not possible because of tidal locking (somehow related to small radius of orbit to keep the moon warm? not quite remember) or the moon atmosphere will be evaporated by the large rogue planet.

So, my question is would the moon of a rogue planet ever have chance like my naive situation exist?(What would be the ideal size of both planet and moon, and their orbital radius?) Or the situation is simply impossible, if so would there be other cases, where the moon of a rogue planet can support life to exist. (may be life within thick ice sheet? or not in the moon but in the planet?)


texts: How does Canada's radiotelescope CHIME manage polarization-dependent apodization of the fast f/0.25 optics?

texts:
CHIME, the Canadian Hydrogen Intensity Mapping Experiment uses four parabolic cylinder reflectors and a dense linear array of 256 x 2 polarization feeds along each focal line. Each feed is a dual polarization cloverleaf. The axes extend north-south (NS) and the cloverleaves appear to have their resolved polarizations EW and NS as well.

My problem is the radiation reaching the cloverleaves from a source at the zenith, reflected from one tip of the parabola to the other is spread out over a 180 degree arc since the parabola is f/D of 0.25. The focal plane is the same height as the edges of the parabola.

imagining the electric field in the NS direction and I imagine a significant cancellation of the electric fields scattered from the east and west tips of the parabolas. If the incident wave is coming down vertically and it's electric field is pointed E, the ray from the east tip may be pointed up, while that from the west tip would be pointed down, so these would tend to cancel leaving the effective aperture smaller for this polarization. (An NS polarized ray would not experience this interference.)

I would call this a kind of polarization-dependent apodization.

Why not simply rotate the cloverleaves by 45 degrees so that the two polarizations were matched and there was no polarization-dependent apodization?

I haven't found any details about this in The CHIME Fast Radio Burst Project: System Overview nor in the reference below.

below x2: from The cloverleaf antenna: A compact wide-bandwidth dual-polarization feed for CHIME

Fig. 1. At left, the shape of each petal consists of two perpendicular straight
lines, two 45 degree circular arcs with radius R and one half an ellipse. W is
the major axis of the ellipse and L is the length from the intersection of the
straight sides to the outer edge of the ellipse. The shape is illustrated here for
the adopted values of gap, R, L, and W. Each of the four tabs shown at the
centre is connected to one side of a vertical microstrip transmission line and
in each case the full width of the adjacent petal is connected to the other lead.
At right, CST simulated currents for one linear polarization at 600MHz are
shown. Note the small asymmetry in the curent distribution near the centre
becasue of the tab geometry.

Fig. 3. A linear array of eight cloverleaf antennas installed at the focal line of
the CHIME Pathfinder at the Dominion Radio Astrophysical Observatory in Penticton, BC, Canada. The picture is taken through the wire mesh reflective surface (mesh spacing 19 mm) illustrating a photonsview of the antennas and ground plane. Notice that each feed has an image-feed in the ground plane, 1/2 λ away at the passband centre frequency. Notice also the four slots cut to remove dielectric material from the gaps between the petals.

below: From https://chime-experiment.ca/instrument

  CHIME consists of four adjacent 20m x 100m cylindrical reflectors oriented north-south. The focal axis of each cylinder is lined with 256 dual-polarization antennas, each of which receives radiation from a large swath of sky that nearly stretches from the northern horizon to the southern horizon. This gives CHIME its enormous field of view. The CHIME antennas are custom-designed to have good sensitivity from 400 to 800 MHz, in both linear polarizations. This gives CHIME its large frequency coverage. Signals from the antennas are amplified in two stages, using low-noise amplifiers developed by the cell-phone industry. This novel application of consumer technology makes CHIME affordable. The 2048 signals from these inputs (256 antennas x 2 polarizations x 4 cylinders) are fed to the F-Engine for the initial stage of digital processing.

below: From SKA_telescope tweet I believe this is looking north.


texts: How are the days relating to right ascension around a polar star chart decided?

texts:
If you look at this link they have days realting to right acension.

How did they calculate nov 20th == 0h, dec 6 == 1h?

I was trying to calculate this in astropy, but I end up with nov 20th, 8pm == 22h.

from astropy import units as u
from astropy.time import Time
from astropy.coordinates import SkyCoord, EarthLocation, AltAz

time_str =  "2017-11-20 20:00"

#Greenville SC, eclipse just went through there.
LON =  -82.3940
LAT = 34.8526
loc = EarthLocation(lat=LAT*u.deg, lon=LON*u.deg, height=0*u.m)

utcoffset = -4*u.hour  # Eastern Daylight Time
obstime = Time(time_str,scale='utc') - utcoffset

cord = SkyCoord(alt=90*u.degree,az=0*u.degree,obstime=obstime,frame = 'altaz',location = loc)
print obstime,cord.fk5.ra.hour, cord.fk5.dec.deg

>> 2017-11-21 00:00:00.000 22.505946538 34.7569396915


texts:
How do you target a radio telescope on the precise object you wish to observe? You can point it in the general direction but how do you get the information from the exact point in the sky that you are investigating?
This seems self evident with an optical telescope but not with a radio telescope.


texts: Moon cycles used for gardening & harvesting

texts:
I appreciate that this question may deviate from the standard astronomy questions.
I have recently read an article that suggest that gardeners, farmers & winemakers etc sometime use the moon's phases to time when best to sow & harvest plants & their fruit. They say that the moisture levels in the soil are higher when there is a full moon exerting its gravitational pull from above & it’s suggested that this helps seeds to sprout. It’s also suggested many winemakers will avoid a full moon at all costs when harvesting the grapes, because although the added moisture in the soil may give you a fuller and juicier grape, this additional water is thought to dilute the taste of the fruit, resulting in a less successful vintage.
Do you think there’s truth in this & that the moon’s gravitation influence affects plant growth & the quality of fruit?
Also, I’m thinking that if this is true, surely it doesn’t need to be a Full Moon because, even during the New Moon & other moon phases the moon may not be visible or only partially visible, but if it’s in the sky above, it’s still exerting its gravitational pull from that direction in the same or similar way. Any ideas or comments most welcome.


texts: What description of the image can we expect from the image of first black hole?

texts:
The EHT has published the first image of a black hole.

I was wondering what could be the size of the original image of the first black hole and the format of the image captured?


texts: Moon's revolution around the Earth and it's rotation around it's axis?

texts: Does Moon rotate around itself while it makes one revolution around Earth or not?


texts: What are the possible solutions to the Red Supergiant problem?

texts:
I have recently come across this so called "Red Supergiant problem" in the literature, a phrase that was coined by Stephen Smartt in 2009 in reference to why red supergiants with masses ∼16-30M⊙ have not been identified as progenitors of Type IIP supernovae.

As I understand it astronomers have observed red supergiants with masses between 8-25M⊙ but only those below ∼16M⊙ have been proven to have undergone a Type IIP supernovae. With the minimum mass required to produce a Wolf-Rayet star at least 25-30M⊙ these red supergiants arent massive enough to be evolving into WR stars either.

There could be systematic errors with the models or calculations and it is well known that calculating the mass of a supernova progenitor post-eruption can be quite a difficult task, but assuming these calculations are correct it leaves a big hole in our understanding of stellar evolution. So my question is, what can explain this gap?


texts: Is there any telescope on Earth that can see the lunar rovers on the moon?

texts: If I have the right numbers, it seems to me that even Hubble telescope might barely be able to make out a carcass of a blue whale on the surface of the moon, which puts objects as small as the lunar rovers or the American flag left there by Apollo out of range. Hubble is often lauded as the best telescope we have built. I know a large part of that is because it is in space where it's free from all of the interference of the atmosphere, but is there any ground-based observatory with better resolution? Is there any place on Earth where I could point a scope at the Sea of Tranquility and see what we left there over 40 years ago?


texts: Discovery in Astronomy vs one in Physics - do they differ in required burden of evidence?

texts:
Discovery in Astronomy/Astrophysics (of astronomical objects) vs discovery of physical phenomena in experimental Physics (as such) - do they differ in required burden of evidence (with the notion, that astronomy/astrophysics deals with real physically existing astronomical objects, while the aim of experimental physics per se is mostly to verify rather somewhat abstract concepts of theoretical physics)?

Perhaps answering my question in some definite way would require some analysis with historical perspective and consideration of precedences ...

This generalized question of mine was motivated by more specific case featured in https://physics.stackexchange.com/q/236107/25575


texts: Where are heavier elements than iron produced?

texts:
Specifically in the milky way, if that changes anything.

I feel like it should be in the disk, since stars there are richer in heavier elements, but I'm not sure.


texts: Diameter of Astronomical Object Using Magnification

texts:
I took a picture of Jupiter through my telescope, using an iPhone. I know the magnification of the telescope lens I used, and can Google to get the magnification of the iPhone lens (the magnification without zooming). Using a standard Photo Editor, I also know the pixels across of Jupiter in my image.

Can I, using all of this information above, calculate how many kilometres one pixel represents, and consequently the diameter of Jupiter?


texts: Does gravitational lensing provide time evolution information?

texts:
When we see multiple images of the same object because of the phenomenon of gravitational lensing, do all the images show the lensed object at the same point in time?

Does it take the same amount of time for light from the lensed object to reach us no matter what image we look at or are we watching the lensed object at different points in time and if so, how big can the difference in time typically be?


texts: Is it possible to do planet observation during the day?

texts: Keep in mind I'm just a newbie. So.... I have a new Newtonian telescope. It has 150mm opening and 1400mm Focal Distance on top of an equatorial mount. I have 25 and 10 mm eyepieces... and a 2x Barlow. I sat down to do observation yesterday and was able to see Saturn and Jupiter (warming up for the alignment on the 21th). Now, I did notice that as they sank closer to the horizon, the effect of the atmosphere was more apparent (and they were less sharp) so I'd like to see if it is possible to see them earlier when they are higher in the sky to try to minimize the effect of the atmosphere... but that might mean to watch them when the sun hasn't set yet. I know that we can't see them with the naked eye when it is daytime but given that the telescope is letting a lot more light in, then it should be possible to see them if I point in the right direction? I intend to use the sun to get RA/DEC alignment (using the telescope shadow, don't intent to look at the sun with the telescope.... yet! :-D) so that then I can point the telescope in the direction of the planets (and I am using Stellarium on my Debian box to get the numbers and stuff).


texts: When the universe expands does it create new space, matter, or something else?

texts: I am wondering what exactly is meant when it is said the universe expands. Does it simply create new space for matter to fill, does it also create new matter/dark matter to fill that space, or am I way off? Thank you for any help!


texts: Sorting out Julian Day, Julian Date, Julian Day number, Julian Day Calendar, and Julian Day Table

texts:
In this answer I mention day number which is 1 on the first day of each calendar year (January 1) and increments to 365 or 366 on December 31 of that year.

There was an edit proposed, which included a sentence explaining that this could be called the Julian Day. I left a message (elsewhere) to the author of the edit I rejected saying:

  Hi, I rejected your edit on this answer because Julian day is not correct. JD is monotonic and is currently 2,458,643.06

to which the author replied

  @uhoh many thanks for the comment! However, there is such a thing as Julian Day of the year. See this NASA web page: https://landweb.modaps.eosdis.nasa.gov/browse/calendar.html

Looking further I saw several similar pages: 1, 2, 3, 4, 5 Some are called Julian Day Calendar and the rest are called Julian Day Table, but each is a table of what I have defined as day numbers, 1 on January 1, and 365 or 366 on December 31.

Could someone help me sort out all of the possible, acceptable terms for the following numbers corresponding to yesterday which include some form of Julian:

Please be generous; include usages that are less common or have fallen out of use but still have some historical use.

2,458,643 (integer)
2,458,643.06  (float)
160  (day number for June 8 on non-leap years)
June 8, 2019


texts: Is the Sun prograde or retrograde with respect to the rotation of the Milky Way?

texts:
I recently learned about the terms prograde and retrograde. I've seen these terms used to describe the rotations and orbits of moons with respect to their planet, and planets with respect to their star. But I haven't been able to find what the relationship is between the rotation and orbit of the Sun with respect to the rotation of the Milky Way.

So, basically what I'm trying to do here is ask two questions:

Is the orbit of the Sun around the center of the Milky Way prograde or retrograde with respect to the rotation of the Milky Way?
Is the axial rotation of the Sun prograde or retrograde with respect to the rotation of the Milky Way?

Regarding question #2, I know it might be considered a slightly weird question to ask, simply because the plane of the Solar System is significantly tilted relative to the plane of the Milky Way (by about 60°), and furthermore the Sun itself has its equatorial plane tilted by a few more degrees relative to the plane of the Solar System (about 7°). But if we mentally "flatten out" the Solar System such that the Sun's equatorial plane aligns with the plane of the Milky Way, then we can talk about whether its axial rotation is in the same direction as the rotation of the Milky Way, so I think this is a valid application of the concept.


texts:
There's exposed water ice on Mars, like in craters like this

At the same time, Mars has dust storm, covering the solar panels of rovers, and occasionally covering the entire planet

So why is this ice not covered in dust?

I understand that dry carbon dioxide ice can maintain a clean surface, as it's seasonally sublimated into the atmosphere and re-deposited, but how come water ice (at least some of it) is also left clean?


texts: Can the Sudarsky's gas giant classification be applied to ice giants?

texts:
Based on the temperature of a gas giant around another star, I have come to understand that it is possible to guestimate its appearance; a classification scheme for gas giants developed by David Sudarky.
I'm wondering if this scheme could plausibly be used to get an idea of what ice giants - Neptune and Uranus like planets - around other stars might look like? If not, are there any resources concerning this topic?


texts: Could a moon of a mini-neptune around a red dwarf harbour life?

texts:
I am planning a game where on could control evolution on an alien world.

I was thinking red dwarf as per here Habitable Planet around Red Dwarf

To my understanding three questions arise:

Tidal lock
Radiation
Sunspots

Could a parent body (think small gas giant) be tidally locked and a moon then freely rotate? Could the magnetic field of a parent body protect a moon from a sun without the parent radiating too much?

I don't know what to say about sunspots though.

Then about the parent body itself:

Is the formation of the mini-neptune so close to a red dwarf impossible? Would its gravity wreck eveything?


texts: How many stars are there max and average per galaxy?

texts:
What is the range of the number of stars possible in a galaxy? What is the rough average?

Googling leads to vague answers, things like "billions upon billions". But what is a more pinpointed set of numbers?


texts:
This answer to Any record of the Earth passing through the tail (not trail) of a comet? mentions

Earth passed through the tail of Halley's Comet in 1910. It caused a bit of a panic due to claims that cyanogen detected in the tail would cause harm: https://en.wikipedia.org/wiki/Halley%27s_Comet#1910

and links to the February 8, 1910 New York Times item Comet's poisonous tail; Yerkes Observatory Finds Cyanogen in Spectrum of Halley's Comet which includes the following sentence:

Only once, as far as known, has the earth passed directly through the tail of a comet, and at that time no unusual phenomena were noticed except that there were abundant showers of meteors.

Question: What comet's tail did Earth pass through before Halley's? This should be a recorded historic event, but it wouldn't necessarily have to have been recognized as such at the time. The goal here is to figure out most likely what event is being described in the quoted sentence.

 (click for larger)


texts: Are there accurate equinox and solstice predictions for the distant past?

texts:
I am trying to find information on the equinox/solstice dates before 1600, more exactly referring up to 10,000 BCE so as to create a sort of calculator on an Excel spreadsheet.

I have read about the SOLEX, but it is not available anymore. Is there any other software that can accurately (as possible, of course) predict the equinoxes and solstices keeping in mind the perihelion/aphelion effects on the period between equinoxes/solstices?

If you believe it is possible to try a formula on excel to calculate these dates for me (instead of just copying down the dates into a database), please keep in mind that my mathematical/programming knowledge is limited.


texts: Is there a ceiling for stable L4 or L5 masses?

texts:
L4 and L5, the Lagrange points 60 degrees leading and trailing an orbiting body, are famous for being stable.

A well known example are the Trojan aseroids at the Sun Jupiter L4 and L5. Nodding to these bodies I label the central mass S, orbiting mass J and the L4 mass T:

It's said S/J needs to be equal to or greater than 24.96 for the system to be stable. For a stable system there's a ceiling on J, it can't be more than 4% of S.

My question: Is there a ceiling on mass T? If T were as massive as J, could the system still be stable?


texts: What is the detection threshold of gravitational waves for LIGO?

texts:
Since now two neutron stars have been detected merging via gravitational waves, I was wondering what is the current detection threshold that the LIGO detectors can achieve.

Considering that the first observed objects were two black holes with a combined mass of more than 60 solar masses and they now detected two neutron stars with a combined mass of only about 3 solar masses I was wondering what was the threshold that these detectors can actually detect.

Obviously there are much larger stars out there which orbit each other, but their size and distance from each other make gravitational waves too difficult to detect. So what masses and at what distances can we expect to be detected in the future?


texts: What are the Similarities and Differences between ALMA and FAST?

texts:
What are the Similarities and Differences between ALMA (Atacama Large Millimeter Array) and FAST (Five hundred meter aperture spherical telescope)?

What can they see, what's their resolution like? How do they compare?


texts: How useful are filters for spotting nebulae?

texts:
Recently I've been trying to spot a couple of nebulae, IC59 and IC1318. The skies at the site are modestly dark (4.5 on the Bortle scale), I'm using an 8" scope, and I've slowly scanned around the areas endlessly with a low magnification/wide angle eyepiece but I haven't been able to find either of them.

Is a filter likely to significantly help in this situation? Would a nebulae filter be more helpful than a light pollution filter?


texts:
Does outer space contain any gases? Recently i watched a video on youtube,in which NASA installs a camera on a spacecraft.The footage shows some dust particles or some matter floating over the space craft's surface and as well from the thrust.What exactly is that? If there is nothing in vacuum,how come newton third law works out to make it move in turn? Here is the link

http://www.youtube.com/watch?v=HSnOTaCeSuk


texts:
According to the first law of thermodynamics, law of conservation of energy states,

The total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.

Question is where was the energy that triggered the big bang at the first place? What are the popular hypotheses?


texts: Why would the Earth's solar analemma would be still a figue eight even if Earth's orbit was circular?

texts:
The Earth's solar analemma is a diagram showing the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth. ... For [a planet] with a circular orbit but significant axial tilt, the analemma would be a figure of eight with northern and southern lobes equal in size.

This statement seems to be true, but it doesn't make any sense to me. If the eight is not due to the equation of time, why is there an eight? Thanks.


texts: Can a supernova or a close passing star create a transient sun gravity focus "habitable zone"?

texts:
This question was inspired by the previous question Would a black hole passing next to a star create a deadly focal point due to gravitational lensing?. I understand, as gravity also acts on light, that any massive object acts as a sort of lens. In the case of our sun, the focal distance starts about 550au, and there are several proposals to send probes there, given we could use the sun as a lens for a huge "telescope". See for example, Hesperides: Solar/nuclear missions to the Sun׳s inner gravity focus and First Stop on the Interstellar Journey:The Solar Gravity Lens Focus.
So I wonder, could the intensity of this effect be enough to melt water and create a sort of habitable zone (perhaps more of a habitable spot) in the opposite direction of a supernova as seen from the sun, by concentrating its light rays. I put the expression habitable zone inside quotes in the title because I don't think that sort of environment would be actually be habitable, as ionizing radiation of the supernova would be concentrated as well, so that would be a extreme environment. Yet, I can think of some interesting observable effects. I think that "habitable spot" would be tiny, but if we were lucky enough for a cometary nucleus pass through it just at the right time, perhapts it could develop a coma that we would be able to observe from Earth. Countless supernovas happened since solar system formation, so I would not be surprised if outer solar system contains a couple remnants of objects roasted this way.
The light of a near passing star would be concentrated too, but I think the effect would be weaker when compared with what a supernova like, say, SN 1054 can achieve.


texts:
Google's definition of a comet is:

  a celestial object consisting of a nucleus of ice and dust and, when
  near the sun, a ‘tail’ of gas and dust particles pointing away from
  the sun.

This doesn't cut it for me. Neither does wikipedia's similar entry.

It pertains to the sun, even though comets are present in other parts of the galaxy other than the solar system and probably other galaxies.

Whats more dwarf planet can be classified as follows:

 * orbits a host star
 * rounded by its own gravity
 * not massive enough to induce thermonuclear fusion
 * not massive enough to clear its region of debris

Which pretty much fits the bill of a comet.

Do you think the following is a fair / recognised classification of a comet:

Comet:
* not rounded by its own gravity
* not massive enough to induce thermonuclear fusion
* not massive enough to clear its region of debris
* composition of ice and dust

But then that's pretty similar to an asteroid:

Asteroid:
* not rounded by its own gravity
* not massive enough to induce thermonuclear fusion
* not massive enough to clear its region of debris

However, this means if an asteroid is comprised of ice and dust, it becomes a comet?

Or are asteroid never comprised of ice and dust? Does my asteroid classification need beefing up, regarding an asteroid's composition?

I'm feeling the comet and the asteroid both need some classification pertaining to their orbit as well? Though thats tricky because only some comets and asteroid, so they're similar in that regard as well! Maybe more details on each objsts composition is needed, like I say...


texts: Why Jupiter's Great Red Spot is Reddish?

texts:
The Great Red Spot is a persistent anticyclonic storm, 22° south of Jupiter's equator, but why is it reddish?

From Wikipedia:

  It is not known exactly what causes the Great Red Spot's reddish color.

Are there updated data?


texts: Trisolar syzygy and it's effects on the planet

texts:
Slightly spoilers here, but in the novel The Three-Body Problem, there's a scene in which Civilization #184 is destroyed by the stacked gravitational attraction of the planet's (aptly named Trisolaris) three suns.

This destruction is portrayed as things (like a sword) suddenly getting lighter, and people and buildings starting to float up in the air, as the atmosphere of the planet is being sucked into the three aligned suns. This is explained as being a "Trisolar Syzygy".

However, I don't understand how that is possible. As I understand it, a syzygy happens in any sort of gravitational alignment of some astronomical bodies, and it's apparently what generates the tidal variation on the earth from the moon's orbit. But would the tidal forces be enough to cause this effect?

In the novel, the planet is in the Alpha Centauri system, which may have a planet in the habitable zone, and is an actual trinary system. Could such an astronomical event actually cause some effect like that in this situation?

I'm asking this here because I thought it wouldn't fit in the Science Fiction Q&A, as I'm more interested in the astronomical side of it, but I'd appreciate a pointer if I don't need to ask this here.


texts: Is there a name for the maximum in local solar elevation angle?

texts:
It came up in conversation today that we were nearly at 21st June, and the days would shortly be getting, um, shorter.

We were trying to think of the the term that means "When the sun is at the highest point it can attain in the sky during the year", as opposed to during the day, (which is the solar noon). We have terms like Perigee and Apogee, it seems (to me) that there should be a name for this as well.

Is there?


texts: How did Mars come to have a 24 hour 39 minute day?

texts: Mercury rotates three times for every two revolutions around the Sun, apparently due to a gravitational resonance with the Sun.Venus takes about 225 days to rotate, and rotates in the opposite direction of any of the inner planets. Maybe because its extreme nature makes it ornery.Earth rotates once every 24 hours, a condition caused by the tidal interaction between Earth and its Moon. It's believed that the Earth was rotating about once every 5 hours before the theorized collision with a Mars sized coorbiting object referred to as Theia.Mars shows no signs of a similar collision. Its two moons appear to be asteroids that were captured from the asteroid belt. So how did Mars come to have a day so close to the length of an Earth day?


texts:
Degenerate matter (neutronium) is hypothesized to be very dense and, at a certain amount, unstable - in the sense of collapsing on itself and causing fusion. The result would be a massive fusion detonation. Such a detonation could cause the Sun to lose its photosphere and cook the inner Solar System with a wave of radiation. This event is described enjoyably in Robert Sawyer’s book, "The Oppenheimer Alternative". The discovery of the neutron core, however, is made by identifying a transient rise in products of the CNO fusion cycle which is hypothesized to require 20 million Kelvin, whereas the Sun’s core temperature is ‘only’ 15 million Kelvin. These fusion products are detected by solar spectroscopy.
Can such a neutron core exist? If it did exist, how could the by products of the CNO cycle be identified before the actual explosion? I mean, if the neutronium degenerates, fuses, and raises the Sun's temperature to allow CNO fusion, then isn't the explosion going to happen before any of the photons from the explosion have time to heat the Sun up enough to make CNO products detectable in the spectra?
EDIT: Fortunately there are many people here who are smarter than me and still kind enough to show it nicely. I will try to clarify the facts of the novel without spoilers (Rather like describing the phenomena of Red Matter in Star Trek (2009) without spoiling the plot)

Edward Teller presents three spectra of the sun taken in 1929,1938 and 1945 at a colloquium in Los Alamos
Fermi remarks that the second spectrum is not of our sun but of an F class star because of the strong carbon absorption lines
Teller infers that something happened to our sun around 1938 to heat it up a little to spark off C-N-O fusion
Oppenheimer relates von Neumann's weather data that the Earth was indeed statistically warmer during that 'period'. He goes on to say that the problem is not with the spectrograph plates from Bethe nor the math done by Teller. Rather, Oppenheimer says that the sun is indeed having a 'problem'
Oppenheimer recalls publications from Zwicky and Landau that hypothesized a neutron core to our sun.
Oppenheimer recalls a paper he wrote with Robert Serber that refuted Landau's work with calculations that a neutron core greater than 0.1 solar masses would be unstable.
Neutron core instability would manifest as a hotter sun
Oppenheimer starts to say that such instability is transient and Teller interrupts him to blurt out that the unstable neutronium would be ejected from the sun
Teller goes on to say that a neutron core would be formed by an implosion, then compares it to the process that happens in the atomic bomb,FatMan, where an explosive array is used to implode a plutonium core. The inevitable result he states is an explosion (It is unclear if he means fission or perhaps his own demon, fusion)
Hans Bethe then calculates that based on the expected size of a neutron core, the known size of the sun, and the opacity of the sun that the outwardly exploding degenerate matter would hit the photosphere in 90 years.

At this point, I will let the other really knowledgeable people here comment on these points and their veracity. However, I am still haunted by the idea that a small really heavy object (microscopic black hole, white dwarf, etc) could be captured by our sun and then precipitate instability.


texts: How to calculate the light energy of a supernova?

texts: I have been given a distance, an average flux, and a time period. How do I find the light energy emitted of a supernova over that time period?


texts: Is there a significant population of neutron stars outside the galactic plane?

texts:
Pulsar kicks originating from supernovae can impart neutron stars with speeds of 100-500 km/s, often at or close to the escape velocity of the Milky Way. Even if a pulsar fails to escape the galaxy, it can be launched into unusual orbits. Assuming that the velocity distribution is isotropic, a decent fraction of such pulsars should have large orbital inclinations after the kicks, such that they rise above the galactic plane.

I have two questions regarding this:

Is there a large - i.e. noticeable - population of such neutron stars, distinguishable by modern telescopes, or is the fraction of total neutron stars relatively small?
Does observing a pulsar - at any wavelength - in such an orbit have any advantages over observing an identical pulsar firmly in the galactic disk? I would assume that some kicks could propel them high enough that scattering along the line of sight could be lessened, leading to a smaller dispersion measure smearing, and could also isolate the pulsars from ambient radio sources in the disk, such as a the galactic center.

I understand that "noticeable", at the least, is a bit subjective, but I can't come up with any non-arbitrary criteria to change that.


texts: Which elements are an indication of habitable exoplanets?

texts:
Using spectroscopy the chemical composition of exoplanets atmosphere is determined. As a scientist, what spectral lines would you look for?

Which elements are relevant in pursue of a second earth?


texts: At what distance from Earth would our Sun be the same apparent magnitude as the next brightest star in the sky?

texts:
When I stand outside looking at the night sky, to my untrained eye, everything except the moon looks like a star.  I know intellectually that some are planets circling our sun, and some are entire galaxies far away, but they all look basically the same.

How far out do you have be be from our sun for it to appear the same as any other 'star' in the sky?

Edit to clarify

As we migrate out through the solar system, when we look up to the sky the sun will get dimmer the farther away we get. On earth there is no doubt which star is our sun.

As we occupy bodies in the solar system farther from the sun, where will we be when the sun appears to be the same brightness as any other star in the sky?


texts:
The telescope I'm using is a National Geographic 76 Diameter, 700 focal length, Equatorial Mount.

It's hard to use the equatorial mount, as this is my first telescope it's hard to use.

Everything I see is upside down.

I don't know how to polar align my telescope.

I don't know how to make move the telescope around properly because of this EQ mount.

Any help would be really appreciated

I watched videos of people aligning their finderscope but i don't even know how to move mine let alone align it.


texts: Where can I download processed data of the Kepler telescope?

texts: I search for lightcurve Kepler data: time $t_i$, flux $F_i$ and measurement uncertainties $\sigma_i$ I need processed data (after removing trends, normalized, etc.).  Where can I find it?


texts: How will nearby galaxies some day expand beyond our horizon? (Neil deGrasse Tyson)

texts:
In his appearance on Television contained in the video The Mystery That Keeps Neil deGrasse Tyson Up At Night, Astronomer andeducator Neil deGrasse Tyson says:

I don’t want to be blamed if you can not get to sleep tonight.
This dark energy, in the future, will render the universe so large, having accelerated so significantly, that all the galaxies of the night sky will have accelerated beyond our horizon.
All the galaxies are the source of our knowledge of the big bang.
Everything we know about the history of the universe comes to us from these galaxies.
If they accelerate beyond our horizon, the next generation of cosmic explorers will only have the stars of the milky way to think about.

What does this mean, in simple terms if possible. How will nearby galaxies some day expand beyond our horizon (if that's what he's saying and if it is correct)?


texts: What kind of radiation do supernova remnants emit?

texts: Do supernova remnants emit EM radiation? Moreover can neutrinos be emitted by these remnants?


texts:
Watching this youtube video shows that our planet is nothing more than dust in the wind.

At the 2:50 mark in the video, you will see a view of the whole Milky Way. At the bottom you will see this text

Light travel time from earth: 100,000 years

Which means if we travel at light speed we need 100,000 years to go far from the Milky Way.

If nothing can travel faster than light, and if it takes 100,000 years to go far from the Milky Way at light speed

How did they map our whole universe, which has a radius of 13.798±0.037 billion light years?


texts: Troop of moving stars through a straight line

texts: Last night,I and my brother suddenly saw that some(50-60) dots of light( exactly like stars)  were moving through a straight line(from NW to SE) above us  with same velocity and towards exactly same directions.These moving stars were seen for just a few seconds.Then they didn't disappear, they just crossed us. We became confused. My brother is highly interested in astronomy. But he was unable to detect the phenomenon. I think this case is rare.  What may they be?


texts: What's the oldest possible age of the universe? (LCDM parameter range)

texts: What would happen if you took today's six-parameter LCDM model down to the 5% confidence level?  Understanding that the number of permutations is high, I would be particularly interested just in the present age of the universe t0---- what are t0's higher and lower limits, assuming that all five of the other parameters are leaning all the way to the plausible floor at the 5% CL either to increase t0 together, or to decrease t0 together?


texts: Would one have to be more than halfway to the Oort Cloud for the Sun to appear as bright as the full moon?

texts: Is this correct?  If the Sun is 400,000 times brighter than the full moon am I correct in figuring that one would have to be about 632AU from the Sun for it to appear as bright as the full moon.  If the Oort Cloud begins about 1000AU from the Sun, one would have to be more than 60% the way to the Oort Cloud for the Sun to appear as bright as the full moon.


texts: How do pressure, temperature, and gravity affect a smaller body than Earth with the same bulk composition?

texts: Earth has a density of about ${\rm 5.513 ~g/cm^3}$ with one Earth radius and one $g$.  Venus, a very similar planet to Earth and likely with about the same bulk composition, has a density of about ${\rm 5.24 ~g/cm^3}$ with 0.95 Earth radii and $0.9 \cdot g$.  How does this scale?  If a planet has 0.5 Earth radii, how would the lower core pressure, lower temperature, and lower gravity impact the density based on the same bulk composition?


texts: How can we infer the mass of SMBH in galaxies that are not active anymore?

texts:
I know it is possible to infer the mass of a supermassive black hole (SMBH) by many methods, i.e., stellar orbits for out Galaxy, Iron line profile from the accretion disk, and probably other methods (perhaps from the spectrum of the radiation disk itself, that can be related with the central mass, if supposed thermal in origin).
What I don't know is: how can we infer the mass of SMBH in galaxies that are not active anymore?


texts: Geographical Substellar position calculation from RA/DEC

texts:
I was trying to help my son with a project and thought it shouldn't be hard but turned out I'm not as smart as I thought I was.

His project is about celestial navigation. The first step is, given the J2000 ra/dec of a specific star and a UTC time of observation first find the geographical lat/lon ground point (substellar point) for the star.

My assumption was lat = dec and lon was simply the ra - sidereal time from UTC time. So we knocked up a simple program to perform this. Then we used Stellarium (with refraction off for now) to test the output. And the star is indeed overhead but it is always off by a number of minutes. I suspected precession but that seems to be measured in arcseconds per year?

So now I realise my simple assumption isn't correct, only approximate. Could someone more knowledgeable please fill the gap in my knowledge.

Thanks in advance.


texts: What kind of telescope do I need to see most of the Jupiter's moons?

texts: I have a simple Newtonian reflector telescope. Using it, I am able to see the Galilean moons of Jupiter. However, Jupiter has much more moons than that (Wikipedia says 67 have been discovered this far). What kind of telescope I would need to see most or all of them?


texts:
Was comet ISON in a Kepler orbit prior to disintegrating? If so, it is possible over time that Kepler orbits can be altered by increases or decreases in the mass of of celestial bodies?
For instance if ISON was in a Kepler orbit and it lost mass did it maintain its orbit and disintegrate in its orbital track or does it alter its track due to the loss of mass?


texts: What part of the milky way do we see from earth?

texts:
When looking up at the night sky, we can sometimes observe a bright band of stars stretching across it. I know this is our galaxy but exactly what are we looking at?

Could we look at the centre of the galaxy or is there another spiral arm blocking our view?
How does our view change as earth rotates around the sun? (E.g. What part of the milky way do we see in a winter night sky)


texts: Why the chosen orientation for the M87 black hole image?

texts:
By now we are all familiar with the official image of the black hole in M87:

Now, in the universe, as far as I know, there is no up and down, nor left and right. All is relative. Hence my question: why the particular chosen angle of the image released? Why not instead release the image as, for example, below? Which is the point of reference chosen in the original image? Is it of any particular significance?


texts: What is the reason for magnetic braking?

texts:
What is the reason of Magnetic Braking in contact binary stars?
Just dark spots?
I mean hot spots can have this effect on binaries.


texts: How can we ge to the exoplanet Proxima b?

texts: I would like to know please how can we get to the exoplanet Proxima b. I heard it is the potentially habitable exoplanet closet to Earth at only 4.2 light years away. So exciting!


texts: Free source of printable star charts in the format of the Millennium Star Atlas?

texts:
I've been looking for sources of printable electronic star charts - there seem to be many different ones available, either as part of planetarium software or just plain charting packages. But there's such a richness of offerings that I'm having trouble figuring out which of those, if any, can produce printable charts in the format that I'm looking for.

I like the general format of the Millennium Star Atlas - black stars on a white sky background, and with horizontal lines representing 1 degree of declination and vertical lines representing 4 minutes of RA (see sample page at http://www.skyandtelescope.com/wp-content/uploads/GD-Sept2011-Chart.pdf ).

I'd like to be able to specify a range of RA and declination and get that chart.

Can anyone suggest any free star chart printing software that can print similar output for any desired sector of the sky?

I'm looking at Cartes du Ciel (http://sourceforge.net/projects/skychart/) which might have that capability, but if so, I haven't yet figured out how to enable it.


texts: 24th Nov 2019.0515 hrs.GMT +1.saw a line of stars moving in a staright line.straight.what could it be?

texts: While doing our morning navigation watch.. we saw stars moving in line.. it continued for atleast 10 mins.. not a airplane or shooting stars.. Can it be satellites orbiting??


texts: If a person were to die on the Moon or Mars, would the body decompose?

texts: There wouldn't be enough oxygen for any bacteria to decompose the body, right? Not to mention, the radiation of space might kill off most organisms on it. So would it decompose, given millions of years?


texts: In planetary and astronomical science, what exactly is, or is not, a tidal force?

texts:
I'm wondering exactly in which situations forces between bodies are, and are not consider to be tidal forces in the context of planetary and astronomical science.

If two rigid, non-deformable spherical masses with shperically symmetric mass distributions orbit each other,  can we say there are no tidal forces or tidal effects there?

If one of them has a permanent, static deformation (e.g. quadrupole moments and higher) are there tidal forces then? If both do?

Or are dynamic, induced deformations required before we invoke the "T-word"?

Can tidal forces be radial, such that they do not tend to raise or lower an orbit over time, or must they have tangential components, like the one that is slowly raising the Moon's orbit?

Is it possible to draw a clear line here, at least within the scope of this SE site and This month's focus tag which is tidal-forces?

According to that tag's Tag Info:

  There is no usage guidance for this tag … yet!

Slightly related: Constraints on the mass distribution within each body such that their mutual orbits are Keplerian?


texts: What's the differences between one-dimensional spectrum and two-dimensional spectrum?

texts: mostly, we use the one-dimensional spectrum. But sometimes we use two-dimensional spectrum, what's the differences between them?


texts: Einstein General relativity and bending of space

texts:
As Einstein's General relativity suggests that the space
time curves in the presence of matter, which is experimentally
proven too, this phenomenon also explains orbits. My question
is if the presence of mass curves space-time, in which direction
does it bend, if we assume that it bends in one of all possible
directions then what makes the body to choose that particular
direction. Does all the bodies bend the space-time in the same
direction ?


texts: How do we know that 2MASS J0523-1403 is a red dwarf?

texts:
I was reading about red dwarfs, and stumbled upon this article about the least massive red dwarf, and noticed several peculiarities:

The spectral type is L2.5
The luminosity class is V
The mass is 67.54±12.79 Jupiter masses, or 0.0644±0.0122 solar masses.

The first bullet point states that the spectral type is L, a brown dwarf class. Sure, some red dwarfs have spectral type L0-L2, but L2.5 seems a bit too much. Also, the luminosity class is V (main sequence dwarf), not VI or sd (subdwarf). The mass is also way below the red dwarf limit (~85 Jupiter masses). Even if the uncertainty was at its maximum, the mass would fall short by about 3 Jupiter masses.
So, how do we determine/prove that a potential red/brown dwarf is truly a red or brown dwarf? Also, has this 2MASS object been proved to be one or the other?


texts:
Jupiter has a great many moons - in the hundreds, and they're still being discovered.

What is the current theory for where all these moons came from? Are they rocks flying through space captured by Jupiter's gravity?


texts:
I was going through the zoomable image of Milky way and after zooming to this particular location, we can see a reddish area on the left side of a probably large star. Here is a screenshot I took after zooming to that particular area:

So is this gas cloud or some weird lens effect ?

Edit: Location ( center of the blue rectangle )


texts: Is there a way to tell what the surface of a planet is like?

texts:
Kepler-442b

I'm doing a project in which I need to find a planet within our galaxy that might be habitable. I found this planet that is within its stellar system's habitable zone, and due to research I have found that this planet is one of the closest in similarity to Earth, in terms of size, and temperature. But I don't really know anything about the surface or physical features.

I think there is an equation to find if there is life on another planet, but I cant find anything about water...

If you can help me, thank you so much.

I need to know the physical and chemical features on a planet's surface. I know the planet is within the habitable zone and is thought to contain water, but I need more detail, if there is any way to get the specific or at least highly probable features of the surface. Sorry I didn't make this clear enough.


texts: What suggests the cyclic nature of the universe? Proposed by Stephen Hawking

texts:
In "A Briefer History of Time" by Stephen Hawking he writes that if we were to travel faster than the universe were expanding and for long enough (in a straight line) we would eventually come back to the point we started.

What suggests that the universe is cyclic in nature as this suggests?
Or what led him to come to this conclusion?


texts: Has any of the orbiters or rover on Mars captured image of comet NEOWISE?

texts: We are seeing stunning pictures of comet NEOWISE from earth (and ISS too), are there any pictures captured from Mars by an orbiter or rover, or any other spacecraft?


texts: Scientists say that gravity warps space and time. They also say that the more gravity there is the slower time moves. Why and/or how does gravity do this.


texts: Does the latitude of your position on earth change the appearance of the cresent like it changes the position of other objects visible in the sky? Does it rotate it?


texts: Is there a place on Earth, where polar axis lies on the horizont and heaven equator is in zenit? If it exists, can I, in theory, see all the constelations available worldwide this night?


texts: Galactic extinction as a function of distance

texts:
I am looking at several galactic sources in the $I$, $R$ and $V$ bands and I want to calculate their absolute magnitudes. I can get the apparent magnitude and I know the distance so I just need to account for extinction to acquire the absolute magnitude. I first used the NED Coordinate Transformation & Galactic Extinction Calculator but the calculated extinction values are too high. I figured that this is probably due to the fact that my sources are relatively close ($\sim 100\,\text{pc}$) and I am thus only looking through a fraction of the dust that these coefficients were calculated for.

If I lower the extinction coefficients to a certain fraction of NED's value (say 60% in a particular case) then I get the expected answer but I'm looking for an accurate way to choose this fraction. I've looked for a method to calculate the extinction coefficients as a function of distance but haven't been able to find anything. Does there exist a map of extinction as a function of distance (and galactic coordinates) in the galaxy from which I can extrapolate the information required? Is there a way to calculate the extinction coefficients ($A_I$, $A_R$ and $A_V$) for an object in the galaxy a known distance away? I found IPHAS which seems to be the right idea but I'm not sure if I can use it to get what I want (or how).


texts: Effect of the absence of atmospheric refraction to sun rise and sunset times

texts:
What is the effect of absence of atmospheric refraction on sin rise and sunset time?
Is it will be delayed or earlier for sunrise and sunset, and why?
Thank you:)


texts: How does an accreting black hole acquire magnetic fields?

texts:
There is actually a similar question on this site: Can magnetism escape a black hole?, however the answers do not focus on accretion, which is my main concern, so I start a new one.

In Kip Thorne's book Black Holes and Time Warps: Einstein's Outrageous Legacy, there is a paragraph in Chapter 9, describing how the central black hole of a quasar (or radio galaxy) acquires a magnetic field through accretion:

  Where do these magnetic field lines come from? From the disk itself.
  All gas in the Universe is magnetized, at least a little bit, and the [accretion] disk's gas is no exception. As, bit by bit, the disk's gas accretes into the hole,
  it carries its magnetic field lines with it. Upon nearing the hole, each
  bit of gas slides down its magnetic field lines and through the horizon,
  leaving the field lines behind, sticking out of the horizon and threading
  it [...]. These threading field lines, firmly
  confined by the surrounding disk, should then extract the hole's
  rotational energy by the Blandford—Znajek process.

Unfortunately this description does not seem clear to me (although Thorne generally is excellent in explaining things throughout the book). To be specific, I cannot get a picture of the gas "sliding down" its magnetic field lines through the event horizon, while making the magnetic field "stick out" of the horizon at the same time. And here Thorne did not seem to point to any original research papers for further study.

So, my questions are:

(1) Do today's astronomers still believe that disk accretion is the main process by which supermassive black holes acquire a magnetic field?

(2) If the answer to (1) is "yes", then how can I build the picture (if there is such a picture) that Thorne is trying to convey in his paragraph?

(3) Is there any research paper that addresses this problem to some detail?

Any help is appreciated!


texts: Is there software to calculate/plot decomposed rotation curves from observational data (FITS, etc)?

texts:
I have observation data of galaxies (in FITS format). From the FITS data, I want to calculate & plot the decomposed rotation curves as pictured below. Is there a software package that will do that (preferably in Python)?
Context: I'm interested in finding the radial mass distribution of the dark matter in each galaxy. If there is already a database or catalog of this, then telling me that would be even better.
[Image from: Roos, Matts. (2010). Dark Matter: The evidence from astronomy, astrophysics and cosmology. ]


texts:
How to plot Doppler profile corresponding to the spectral line? The spectral line was plotted from data: flux with respect to wavelenght and I know the temperature.

These two function are Doppler profile? What should I substitue for $\Delta \nu_{th}$, $\nu_0$ and $\Delta \nu$. These values are from wavelenght according to $\lambda = \frac{c}{\nu}$?

https://en.wikipedia.org/wiki/Doppler_broadening

Or could you recommend me another formula for plotting Doppler profile?


texts: What is the orbital velocity of Pluto around the Pluto-Charon barycenter?

texts: I know the formula for orbital velocity but that doesn't seem of much help when I'm trying to calculate how fast the primary wobbles, or since the barycenter is outside Pluto in the Pluto-Charon system, how fast it orbits.


texts: We know that the Moon's gravity is about one-sixth that of Earth. Then I recently read that the mass of the Moon is about one-eightieth the mass of Earth. Since gravity depends on the mass of the 2 objects, shouldn't the Moon's gravity be one-eightieth the gravity of Earth? Is the Moon extra dense?